The present invention relates to the field of circuits, and in particular, to a method and apparatus for a power-on reset circuit with improved power management.
Digital circuits often use a power-on reset (POR) signal for resetting the digital circuitry during power-up. As the power supply signal approaches a stable operating potential, the POR signal is used to reset, or initialize, the digital circuitry. During operation, the digital circuit may suddenly lose the power supply signal, or the power supply signal may destabilize. The POR signal is used again to reset the digital circuitry until the power supply signal again reaches the stable operating potential. The digital circuitry often reset by a POR signal, includes circuits such as the CMOS logic gates, memory, flip-flops, and timing signal generators. Analog circuits may also use a POR signal to disable certain circuits until a stable power supply signal is available. Using a POR signal ensures proper operation of the analog circuit.
A low voltage detector may be used to detect when the power supply signal decreases below a predetermined potential. The predetermined potential is often chosen according to the minimum operating potential of the circuit. The POR circuit may be used in conjunction with the low voltage detector to reset the circuit at appropriate times.
In accordance with the invention, a power-on reset circuit provides a power-on reset signal that includes a rising and falling edge. The rising and falling edges of the power-on reset signal have associated rising edge and falling edge trip points. The rising edge trip point can be used to reset internal components of a logic circuit. The falling edge trip point can be used as a low voltage detection signal, indicating when a power supply has decreased below a predetermined potential. The falling edge trip point is adjustable in relation to the potential of the power supply to improve the power management.
Briefly stated, a method and apparatus is directed to a power-on reset circuit for providing a power-on reset signal having a rising edge and an adjustable falling edge. A reference generator circuit produces two different reference signals in response to a power supply signal. The two reference signals are compared by a comparison circuit to produce a resulting reference signal. The resulting reference signal tracks the power supply signal until a first threshold potential is reached. When the first threshold potential is reached, a rising edge is produced in the power-on reset signal. The rising edge indicates that the power supply signal has reached an operating potential. A second threshold potential corresponds to the adjustable falling edge of the power-on reset signal. When the power supply signal decreases below the second threshold potential, the adjustable falling edge is produced in the power-on reset signal. The second threshold potential is adjusted when an adjustment circuit selectively couples additional transistors to the reference generator circuit. The additional transistors change the level of the second threshold potential in relation to the power supply signal. Adjusting the second threshold potential adjusts the falling edge of the power-on reset signal. The falling edge may operate as a low voltage detector by indicating that the power supply signal has decreased below its operating potential.
An embodiment of the invention is directed to an apparatus, generating a power-on reset signal, wherein the power-on reset signal has a rising edge and an adjustable falling edge, that includes a reference generator circuit. The reference generator circuit is arranged to produce a first reference signal and a second reference signal in response a power supply signal. A comparison circuit is arranged to produce a resulting reference signal in response to a comparison between the first reference signal and the second reference signal. The resulting reference signal depends upon a first threshold potential and a second threshold potential of the power supply signal. A detector circuit is arranged to produce the power-on reset signal in response to the resulting reference signal. The rising edge occurs in the power-on reset signal when the power supply signal increases above the first threshold potential and the adjustable falling edge occurs when the power supply signal decreases below the second threshold potential. An adjustment circuit is arranged to adjust the adjustable falling edge of the power-on reset signal in response to the resulting reference signal. The adjustable falling edge is adjusted by changing the second threshold potential.
Another embodiment of the invention is directed to a method for producing a power-on reset signal with improved power management. The method includes: generating a first reference signal that relates to a power supply signal, generating a second reference signal that relates to the power supply signal, comparing the first reference signal to the second reference signal, producing a resulting reference signal with an associated potential at a node in response to the comparison of the first reference signal to the second reference signal, detecting the associated potential of the resulting reference signal, triggering a first edge in the power-on reset signal in response to the associated potential of the resulting reference signal when the power supply signal crosses a first threshold potential, triggering the second edge in the power-on reset signal in response to the associated potential of the resulting reference signal when the power supply signal crosses a second threshold potential that is different from the first threshold potential, and adjusting the second edge in the power-on reset signal by adjusting the second threshold potential.
Yet another embodiment of the invention is directed to an apparatus, providing a power-on reset signal with an adjustable second edge. The apparatus includes a means for generating a first reference signal that is arranged to generate a first reference signal that relates to a power supply signal. A means for generating a second reference signal is arranged to generate a second reference signal that relates to the power supply signal. A means for producing a resulting reference signal is arranged to produce a resulting reference signal with an associated potential in response to the first reference signal and the second reference signal. A means for detecting is arranged to detect the associated potential of the resulting reference signal. A means for triggering a first edge is arranged to trigger a first edge in the power-on reset signal in response to the associated potential of the resulting reference signal when the power supply signal crosses a first threshold potential. A means for triggering the second edge is arranged to trigger a second edge in the power-on reset signal in response to the associated potential of the resulting reference signal when the power supply signal crosses a second threshold potential, wherein the second threshold potential is different from the first threshold potential. A means for adjusting is arranged to adjust the second edge in the power-on reset signal by adjusting the second threshold potential.
A more complete appreciation of the present invention and its improvements can be obtained by reference to the accompanying drawings, which are briefly summarized below, to the following detail description of presently preferred embodiments of the invention, and to the appended claims.